Method for making lithographic printing plates

ABSTRACT

Lithographic printing plate are formed by imagewise exposing a positive-working lithographic printing plate precursor with infrared radiation to form an imaged precursor comprising exposed regions and non-exposed regions, and processing the imaged precursor to remove the exposed regions using a processing solution having a pH of 12 or more, that contains a metal cation M 2+  selected from barium, calcium, strontium, and zinc cations, and is substantially silicate-free. The positive-working lithographic printing plate precursor comprises a grained and anodized aluminum-containing substrate, a first ink receptive layer comprising at least one water-insoluble, alkali solution-soluble or -dispersible first resin, a second ink receptive layer disposed over the first receptive layer, and an infrared radiation absorber in an amount of at least 0.5 weight %, in either or both of the first ink receptive layer and the second ink receptive layer.

RELATED APPLICATION

Reference is made to commonly assigned U.S. Ser. No. 13/602,367 (filedSep. 4, 2012 by Hauck, Dietmar, and Savariar-Hauck) that is now grantedas U.S. Pat. No. 8,936,899, and the disclosure of which is incorporatedherein by reference in its entirety.

FIELD OF THE INVENTION

This invention relates to a method for providing lithographic printingplates from corresponding dual-layer positive-working lithographicprinting plate precursors using infrared radiation imagewise exposureand unique processing conditions.

BACKGROUND OF THE INVENTION

In conventional or “wet” lithographic printing, ink receptive regions,known as image areas, are generated on a hydrophilic surface. When thesurface is moistened with water and ink is applied, the hydrophilicregions retain the water and repel the ink, and the ink receptiveregions accept the ink and repel the water. The ink is transferred tothe surface of a material upon which the image is to be reproduced. Forexample, the ink can be first transferred to an intermediate blanketthat in turn is used to transfer the ink to the surface of the materialupon which the image is to be reproduced.

Imageable elements (lithographic printing plate precursors) useful toprepare lithographic printing plates typically comprise one or moreimageable layers applied over the hydrophilic surface of a substrate.The imageable layers include one or more radiation-sensitive componentsthat can be dispersed in a suitable binder. Alternatively, theradiation-sensitive component can also be the binder material. Followingimaging, either the imaged regions or the non-imaged regions of theimageable layer are removed by a suitable developer, revealing theunderlying hydrophilic surface of the substrate. If the imaged regionsare removed, the imageable element is considered as positive-working.Conversely, if the non-imaged regions are removed, the imageable elementis considered as negative-working. In each instance, the regions of theimageable layer (that is, the image areas) that remain areink-receptive, and the regions of the hydrophilic surface revealed bythe developing process accept water and aqueous solutions, typically afountain solution, and repel ink.

Direct digital or thermal imaging has become increasingly important inthe printing industry because of their stability to ambient light. Thelithographic printing plate precursors used for the preparation oflithographic printing plates have been designed to be sensitive to heator infrared radiation and can be exposed using thermal heads of moreusually, infrared laser diodes that image in response to signals from adigital copy of the image in a computer a platesetter. This“computer-to-plate” technology has generally replaced the formertechnology where masking films were used to image the elements.

These imaging techniques often require the use of water or a developer(neutral to alkaline pH) as a processing solution to remove exposed(positive-working) or non-exposed (negative-working) regions of theimaged layer(s). In general, the processing solution is specificallydesigned for the specific radiation-sensitive chemistry in the imagedprecursor and to provide processing as cleanly as possible.

During processing of imaged lithographic printing plate precursors, someprocessing solutions cause corrosion of aluminum-containing substratesand the industry has been investigating means for reducing or preventingcorrosion. For example, some processing solutions contain variouscorrosion inhibitors and in other instances, the aluminum-containingsubstrates are pretreated to reduce corrosion.

Some commercial dual-layer positive-working lithographic printing plateprecursors are imagewise exposed using infrared radiation and thenprocessed with a processing solution containing a silicate as acorrosion inhibitor as described for example in U.S. Patent ApplicationPublications 2004/0063036 (Takamiya) and 2009/0162783 (Levanon et al.).However, it is well known that silicate-containing processing solutionsbecome “dirty” with sludge after continued use. In addition, whensilicate dries in the processing solution tank or other parts of theequipment, carbon dioxide from the air neutralizes the silicate to formcrusted silicon dioxide that is difficult to remove during maintenanceoperations.

Other commercial plate makers design positive-working lithographicprinting plate precursors for processing with processing solutionscontaining non-reducing sugars as corrosion inhibitors as noted also inU.S. Patent Application Publication 2004/0063036 (noted above). However,these materials are generally less effective than silicates and areeffective only with aluminum-containing substrate that have beenpretreated for example using a post-anodic phosphate/fluoride treatmentsolution that itself is prone to form insoluble deposits on rollers andequipment surfaces used in the post-anodic treatment process, and thusrequires frequent laborious cleaning.

It would be desirable to process imagewise exposed positive-workinglithographic printing plate precursors using processing solutions thatare substantially free of silicate, without requiring that theprecursors be made using a dirty post-anodic treatment process.

SUMMARY OF THE INVENTION

The present invention is directed to the noted problems with a methodfor forming a lithographic printing plate, the method comprising:

-   -   imagewise exposing a positive-working lithographic printing        plate precursor with infrared radiation to form an imaged        precursor comprising exposed regions and non-exposed regions,        and    -   processing the imaged precursor to remove the exposed regions        using a processing solution to provide a lithographic printing        plate,

wherein the positive-working lithographic printing plate precursorcomprises:

a grained and anodized aluminum-containing substrate,

a first ink receptive layer that is disposed over the grained andanodized aluminum-containing substrate, the first ink receptive layercomprising at least one water-insoluble, alkali solution-soluble or-dispersible first resin,

a second ink receptive layer disposed over the first receptive layer,the second ink receptive layer being the outermost layer in thepositive-working lithographic printing plate precursor, and comprising asecond resin that is a phenolic resin that is different from thewater-insoluble, alkali solution-soluble or -dispersible first resin,and

an infrared radiation absorber in an amount of at least 0.5 weight %, ineither or both of the first ink receptive layer and the second inkreceptive layer,

wherein the processing solution contains a metal cation M²⁺ selectedfrom calcium, barium, strontium, magnesium, nickel and zinc cations ascorrosion inhibitors, has a pH of at least 12, is substantially free ofsilicate, and is optionally substantially free of reducing sugar.

The first and second ink receptive layers are specifically designed forimproved resistance to pressroom chemicals and for scratch and abrasionresistance without loss of photospeed, image contrast, or imagedurability. Moreover, corrosion is reduced during processing even withaluminum-containing substrates that are prepared without dirtypost-anodic treatments. Thus, sludge and silicon dioxide crusting arereduced.

DETAILED DESCRIPTION OF THE INVENTION

The following discussion is directed to various embodiments of thepresent invention and while some embodiments can be particularly useful,the disclosed embodiments should not be interpreted or otherwiseconsidered to be limited the scope of the present invention, as claimedbelow. In addition, one skilled in the art will understand that thefollowing disclosure has broader application than is explicitlydescribed and the discussion of any embodiment is not intended to limitthe scope of the present invention to any described embodiment.

Definitions

As used herein to define various components of the various ink receptivelayers (and coating formulations) and processing solutions, unlessotherwise indicated, the singular forms “a”, “an”, and “the” areintended to include one or more of the components (that is, includingplurality referents).

Each term that is not explicitly defined in the present application isto be understood to have a meaning that is commonly accepted by thoseskilled in the art. If the construction of a term would render itmeaningless or essentially meaningless in its context, the term'sdefinition should be taken from a standard dictionary.

The use of numerical values in the various ranges specified herein,unless otherwise expressly indicated otherwise, are considered to beapproximations as though the minimum and maximum values within thestated ranges were both preceded by the word “about”. In this manner,slight variations above and below the stated ranges can be used toachieve substantially the same results as the values within the ranges.In addition, the disclosure of these ranges is intended as a continuousrange including every value between the minimum and maximum values.

Unless the context indicates otherwise, when used herein, the terms“lithographic printing plate precursor”, “positive-working lithographicprinting plate precursor”, and “precursor” are meant to be references toembodiments used in the present invention.

The term “support” is used herein to refer to an aluminum-containingmaterial (web, sheet, foil, or other form) that is then treated toprepare a “substrate” that refers to the hydrophilic article upon whichink receptive layers are disposed.

The term “post-treatment” refers to contacting the grained and anodizedaluminum-containing support with an aqueous solution at an appropriatetemperature for a period of time, followed by rinsing and drying, beforeany ink receptive layer formulations are applied.

The precursors are “double-layer precursors” having two ink receptivelayers identified as a first receptive layer nearest the substrate and asecond ink receptive layer that is disposed over the first receptivelayer. In some literature, the first ink receptive layer is known as the“inner” or inside imageable layer, and the second ink receptive layer isknown as the “outer” or outside imageable layer.

The term “ink receptive”, as applied to the layers in the precursors,refers to a coating or layer material to which, after imaging anddevelopment, lithographic ink is attracted.

Unless otherwise indicated, percentages refer to percents by dry weightof a composition or layer, or % solids of a solution or formulation.

As used herein, the term “infrared” refers to radiation having awavelength of at least 700 nm and higher. In most instances, the term“infrared” is used to refer to the “near-infrared” region of theelectromagnetic spectrum that is defined herein to be at least 700 nmand up to and including 1400 nm.

For clarification of definitions for any terms relating to polymers,reference should be made to “Glossary of Basic Terms in Polymer Science”as published by the International Union of Pure and Applied Chemistry(“IUPAC”), Pure Appl. Chem. 68, 2287-2311 (1996). However, anydefinitions explicitly set forth herein should be regarded ascontrolling.

Unless otherwise indicated, the terms “polymer” and “polymeric” refer tohigh and low molecular weight polymers including oligomers and includeshomopolymers and copolymers.

The term “copolymer” refers to polymers that are derived from two ormore different monomers, in random order along the polymer backbone.That is, they comprise recurring units having different chemicalstructures.

The term “backbone” refers to the chain of atoms in a polymer to which aplurality of pendant groups can be attached. An example of such abackbone is an “all carbon” backbone obtained from the polymerization ofone or more ethylenically unsaturated polymerizable monomers. However,other backbones can include heteroatoms wherein the polymer is formed bya condensation reaction or some other means.

As used herein with reference to the processing solutions, the term“silicate” is meant to include both silicate and metasilicate compounds.

Positive-working Lithographic Printing Plate Precursors

Grained and Anodized Aluminum-containing Substrate:

In general, the lithographic printing plate precursors are formed bysuitable application of two ink receptive layer compositions to asuitable aluminum-containing substrate to form two ink receptive layers.This aluminum-containing substrate is usually treated or coated invarious ways as described below prior to application of theformulation(s). For example, the aluminum-containing substrate istreated to provide an “interlayer” for improved adhesion orhydrophilicity, and the first ink receptive layer and second inkreceptive layer, are applied over the interlayer.

The aluminum-containing substrate generally has a hydrophilic surface,or a surface that is more hydrophilic than the applied first and secondink receptive layer formulations on the imaging side. Thealuminum-containing substrate comprises an aluminum support that istreated using mechanical graining, electrochemical graining or chemicalgraining to form a desired rough surface, followed by anodizing using asuitable acid to provide the desired anodic oxide surface and a desiredoxide pore diameter. The aluminum sheet is mechanically orelectrochemically grained and anodized using phosphoric acid or sulfuricacid and conventional procedures.

For example, an electrochemically grained aluminum support can beanodized in a direct current passing through a sulfuric acid solution(5-30 weight %) at a temperature of at least 20° C. and up to andincluding 60° C. for at least 5 seconds and up to and including 250seconds to form an oxide layer on the metal surface. Generally, sulfuricacid anodization is carried out to provide an aluminum oxide layer of atleast 0.3 g/m² and typically at least 1 g/m² and up to and including 10g/m², or up to and including 5 g/m².

The sulfuric acid formed aluminum oxide layer generally has fine concaveparts that are sometimes referred as “micropores” or “pores” that aredistributed, perhaps uniformly, over the layer surface. The density (orvacancy) is generally controlled by properly selecting the conditions ofthe sulfuric acid anodization treatment. The pores can appear as columnswithin the aluminum oxide layer, as viewed in a cross-sectionalmicro-image.

An interlayer is formed or disposed directly on the grained and anodizedaluminum-containing substrate by treatment of the grained and anodizedaluminum-containing support with an aqueous solution (hereafter referredas PAT solution), followed by rinsing and drying. A particularly usefulPAT solution comprises a homopolymer of vinyl phosphonic acid,poly(vinyl phosphonic acid) (PVPA), or a copolymer of vinyl phosphonicacid. A more desirable PAT solution further comprises phosphoric acid. Atypical PAT solution can be prepared by dissolving poly(vinyl phosphonicacid) in water in an amount of at least 0.05 weight % and up to andincluding 20 weight % and phosphoric acid in an amount from 0 to 10weight %.

The thickness of the grained and anodized aluminum-containing substrate(with interlayer) can be varied but should be sufficient to sustain thewear from printing and thin enough to wrap around a printing form. Someembodiments include a grained and anodized aluminum-containing substratethat has a thickness of from at least 100 μm and up to and including 600μm.

The backside (non-imaging side) of the grained and anodizedaluminum-containing substrate can be coated with anon-radiation-sensitive slipping or matte layer to improve handling and“feel” of the lithographic printing plate precursor.

The grained and anodized aluminum-containing substrate can also be in acylindrical form having the poly(vinyl phosphonic acid) interlayer andimageable layer(s) disposed thereon, and thus be an integral part of theprinting press. The use of such imageable cylinders is described forexample in U.S. Pat. No. 5,713,287 (Gelbart) that is incorporated hereinby reference.

First Ink Receptive Layer:

A first ink receptive layer is disposed over the grained and anodizedaluminum-containing substrate described above. In most embodiments, thisfirst ink receptive layer is disposed directly on the substratedescribed above, meaning that there are no intervening layers betweenthem.

The first ink receptive layer comprises at least one water-insoluble,alkali solution-soluble or -dispersible first resin (polymeric binder).Desirably, the first resin is resistant to harsh press chemicals thatcontain strong organic solvents such as glycol ethers and diacetonealcohol. More particularly, the first resin can participate incrosslinking reactions during high temperature baking of the precursorafter imaging and processing.

Useful first resins for the first ink receptive layer include polymerbinders comprising recurring units derived from one or moreN-alkoxymethyl (alkyl)acrylamides or alkoxymethyl (alkyl)acrylates asdescribed for example in U.S. Patent Application Publication2011/0097666 (Savariar-Hauck et al.) and U.S. Pat. No. 8,530,141(Savariar-Hauck et al.), both of which are incorporated herein byreference for details of such polymers and ethylenically unsaturatedpolymerizable monomers from which such recurring units can be derived,including those defined by Structure (II) in the noted publications. Ofthese materials, the N-alkoxymethyl (meth)acrylamides are particularlyuseful and can comprise up to and including 80 weight % of the totalrecurring units in the polymeric binder. Examples of usefulethylenically unsaturated polymerizable monomers include but are notlimited to, N-methoxymethyl methacrylamide, N-isopropoxymethylmethacrylamide, N-n-butoxymethyl methacrylamide,N-isobutoxymethacrylamide, N-t-butoxymethacrylamide,N-ethylhexoxymethacrylamide, N-ethoxymethyl acrylamide, andN-cyclohexyloxymethyl methacrylamide. Useful alkoxymethyl(meth)acrylates include but are not limited to, isopropoxymethylmethacrylate, phenoxymethyl methacrylate, methoxymethyl acrylate,phenoxymethyl acrylate, and ethoxymethyl acrylate.

Other useful polymeric binders (first resins) in the first ink receptivelayer include those described in U.S. Pat. No. 7,858,292 (Bauman et al.)that comprise recurring units comprising pendant 1H-tetrazole groups,which reference is incorporated herein by reference for the details ofsuch polymeric binders.

Mixtures of one or more first resins comprising recurring units derivedfrom N-alkoxymethyl (alkyl)acrylamides with one or more polymericbinders comprising recurring units comprising pendant tetrazole groupscan be used if desired. Alternatively, the polymeric binders cancomprise recurring units derived from N-alkoxymethyl (alkyl)acrylamidesand recurring units comprising pendant tetrazole groups. In suchpolymeric binders, the recurring units derived from the N-alkoxymethyl(alkyl)acrylamides can be present in an amount of at least 2 weight %and up to and including 80 weight %, and the recurring units comprisingpendant tetrazole groups can be present in an amount of at least 5weight % and up to and including 80 weight %. Such polymeric binders canalso comprise recurring units having pendant cyano groups (for example,at least 10 weight %) and other recurring units having pendant carboxy,phospho, or sulfo groups, or recurring units derived from Structures D1through D5 of U.S. Patent Application Publication 2009/0042135 (Patel etal.) that is incorporated herein by reference for these recurring units.

In general, each first resin has an acid value of at least 30 mg KOH/gof polymeric binder or an acid value of at least 40 mg KOH/g ofpolymeric binder and up to and including 150 mg KOH/g of polymericbinder. Acid value can be determined using known methods.

In the lithographic printing plate precursors, the one or more firstresins are present in the first ink receptive layer an amount of atleast 10 weight % and typically of at least 20 weight % and up to andincluding 100 weight % of the first ink receptive layer total dryweight.

The first ink receptive layer can additionally comprise one or moresurfactants, dispersing aids, humectants, biocides, viscosity builders,drying agents, defoamers, preservatives, antioxidants, colorants, ororganic or inorganic particles, all in amounts that are known in theart.

The first ink receptive layer can be formed by applying a first inkreceptive layer formulation to the interlayer of the grained andanodized aluminum-containing substrate using conventional coating orlamination methods. Thus, the formulation can be applied by dispersingor dissolving the desired ingredients (one or more first resins andinfrared radiation absorber, described below, if present) in a suitablecoating solvent, and the resulting formulation is applied to theinterlayer of the grained and anodized aluminum-containing substrateusing suitable equipment and procedures, such as spin coating, knifecoating, gravure coating, die coating, slot coating, bar coating, wirerod coating, roller coating, or extrusion hopper coating. The first inkreceptive formulation can also be applied by spraying it onto aninterlayer.

The dry coating weight for the first ink receptive layer can be at least0.5 g/m² and up to and including 2.5 g/m² and typically at least 0.6g/m² and up to and including 2 g/m².

The selection of solvents used to coat the first ink receptive layerformulation depends upon the nature of the polymeric materials and othercomponents in the formulations, and can include acetone, methyl ethylketone, or another ketone, tetrahydrofuran, 1-methoxypropan-2-ol,1-methoxy-2-propyl acetate, and mixtures thereof using conditions andtechniques well known in the art. The coated first ink receptive layercan be dried in a suitable manner.

Second Ink Receptive Layer:

The second ink receptive layer is disposed over the first ink receptivelayer, and in most embodiments, there are no intermediate layers betweenthe first ink receptive layer and the second ink receptive layer andthus, the second ink receptive layer is disposed directly on the firstink receptive layer. In addition, the second ink receptive layergenerally serves as the outermost layer of the positive-workinglithographic printing plate precursor.

Before thermal imaging, the second ink receptive layer is generally notsoluble or removable by an alkaline processing solution within the usualtime allotted for development, but after thermal imaging, the exposedregions of the second ink receptive become soluble in or removable bythe processing solution.

The second ink receptive layer can comprise the compositions of inkreceptive layers in positive-working lithographic printing plateprecursors described for example, in U.S. Pat. No. 6,255,033 (Levanon etal.), U.S. Pat. No. 6,280,899 (et al.), U.S. Pat. No. 6,391,524 (Yateset al.), U.S. Pat. No. 6,485,890 (Hoare et al.), U.S. Pat. No. 6,558,869(Hearson et al.), U.S. Pat. No. 6,706,466 (Parsons et al.), U.S. Pat.No. 6,541,181 (Levanon et al.), U.S. Pat. No. 7,223,506 (Kitson et al.),U.S. Pat. No. 7,247,418 (Saraiya et al.), U.S. Pat. No. 7,270,930 (Haucket al.), U.S. Pat. No. 7,279,263 (Goodin), and U.S. Pat. No. 7,399,576(Levanon), and U.S. Published Patent Applications 2006/0130689 (Timpe etal.), 2005/0214677 (Nagashima), 2004/0013965 (Memetea et al.),2005/0003296 (Memetea et al.), and 2005/0214678 (Nagashima), all ofwhich are incorporated herein by reference.

The second ink receptive layer generally comprises one or more secondresins or polymeric binders that can be the same or different than thefirst resins (polymeric binders) described above for the first inkreceptive layer. Examples of useful second resins include but are notlimited to the polymeric binders described in U.S. Pat. No. 7,163,770(Saraiya et al.), U.S. Pat. No. 7,160,653 (Huang et al.), and U.S. Pat.No. 7,582,407 (Savariar-Hauck et al.).

The second ink receptive layer desirably contains one or more phenolicpolymeric binders as second resins that are generally water-insolublebut soluble in alkaline processing solutions (defined below). The term“phenolic” means a hydroxyl-substituted aryl group.

Useful phenolic polymers include but are not limited to, poly(vinylphenols) or derivatives thereof. They can also include pendant acidicgroups such as carboxylic (carboxy), sulfonic (sulfo), phosphonic(phosphono), or phosphoric acid groups that are incorporated into thepolymer molecule or pendant to the polymer backbone. Other usefuladditional phenolic polymers include but are not limited to, novolakresins, resole resins, poly(vinyl acetals) having pendant phenolicgroups, and mixtures of any of these resins (such as mixtures of one ormore novolak resins and one or more resole resins). Generally, suchsecond resins have a number average molecular weight of at least 3,000and up to and including 200,000, and typically at least 6,000 and up toand including 100,000, as determined using conventional procedures.Typical novolak resins include but are not limited to,phenol-formaldehyde resins, cresol-formaldehyde resins,phenol-cresol-formaldehyde resins, p-t-butylphenol-formaldehyde resins,and pyrogallol-acetone resins, such as novolak resins prepared fromreacting m-cresol or an m,p-cresol mixture with formaldehyde usingconventional conditions. For example, some useful novolak resins includebut are not limited to, xylenol-cresol resins, for example, SPN400,SPN420, SPN460, and VPN1100 (that are available from AZ Electronics) andEP25D40G and EP25D50G (noted below for the Examples) that have highermolecular weights, such as at least 4,000.

Other useful second resins include polyvinyl compounds having phenolichydroxyl groups, include poly(hydroxystyrenes) and copolymers containingrecurring units of a hydroxystyrene and polymers and copolymerscontaining recurring units of substituted hydroxystyrenes. Also usefulare branched poly(hydroxystyrenes) having multiple branchedhydroxystyrene recurring units derived from 4-hydroxystyrene asdescribed for example in U.S. Pat. No. 5,554,719 (Sounik) and U.S. Pat.No. 6,551,738 (Ohsawa et al.), and U.S. Published Patent Applications2003/0050191 (Bhatt et al.), 2005/0051053 (Wisnudel et al.), and2008/0008956 (Levanon et al.). These branched polymers can have a weightaverage molecular weight (M_(w)) of at least 1,000 and up to andincluding 30,000. In addition, they can have a polydispersity of lessthan 2. The branched poly(hydroxystyrenes) can be homopolymers orcopolymers with non-branched hydroxystyrene recurring units.

Some particularly useful second resins are phenolic polyvinyl acetalresins, for example like those described in at least the followingpublications: U.S. Pat. No. 7,399,576 (Levanon et al.) and U.S. Pat. No.7,544,462 (Levanon et al.), and U.S. Patent Application Publications2006/0154187 (Wilson et al.) and 2009/0162783 (Levanon et al.). Otheruseful polyvinyl acetal resins are described in copending and commonlyassigned U.S. Ser. No. 12/555,040 (Levanon et al.).

Still other useful polyvinyl acetal resins can comprise, in randomfashion:

a) vinyl acetal recurring units comprising pendant hydroxyaryl groups,

b) recurring units comprising hydroxyaryl ester groups, or

c) either or both types of recurring units (Ia) and (Ib), in randomfashion.

In such second resins can comprise recurring units represented by eitheror both of the following Structures (Ia) and (Ib), in random fashion:

that are described in more detail below.

Still other embodiments include the use of a second resin thatcomprises, in random fashion, in addition to the recurring units fromStructures (Ia) and (Ib), of at least 25 and up to and including 60 mol% of recurring units represented by the following Structure (Ic):

and optionally up to 25 mol % of recurring units represented by thefollowing Structure (Id), optionally up to 10 mol % of recurring unitsrepresented by the following Structure (Ie), and optionally up to 20 mol% of recurring units represented by the following Structure (If), inrandom fashion, all based on the total recurring units in the polymericbinder:

which Structures (Ic) through (If) are described in more detail below.

In Structures (Ia) and (Ib), R is a substituted or unsubstitutedhydroxyaryl group such as a substituted or unsubstituted hydroxyphenylor hydroxynaphthyl group wherein the aryl group has 1 to 3 hydroxylgroups on the ring. Typically, there is only 1 hydroxyl group on thearyl ring. Other substituents that can optionally be present on the arylgroup include but are not limited to, alkyl, alkoxy, halogen, and anyother group that does not adversely affect the performance of thepolymeric binder in the imageable element. R₂ is a substituted orunsubstituted hydroxyaryl group in which the hydroxyl group is ortho tothe ester linkage. Some of the R₂ groups are substituted with a cyclicimide group, for example a substituted or unsubstituted hydroxyphenyl orhydroxynaphthyl group that has a cyclic imide substituent such as analiphatic or aromatic imide group, including but not limited to,maleimide, phthalimide, tetrachlorophthalimide, hydroxyphthalimide,carboxypthalimide, and naphthalimide groups. Further optionalsubstituents on R₂ include but are not limited to, hydroxyl, alkyl,alkoxy, halogen, and other groups that do not adversely affect theproperties of the cyclic imide group or the polymeric binder in theimageable element. A hydroxyphenyl group, with a cyclic imidesubstituent and no other substituents, is useful in the polymericbinder.

In Structure (Id), R₁ is hydrogen or a substituted or unsubstitutedlinear or branched alkyl group having 1 to 12 carbon atoms (such asmethyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, chloromethyl,trichloromethyl, iso-propyl, iso-butyl, t-butyl, iso-pentyl, neo-pentyl,1-methylbutyl, iso-hexyl, and dodecyl groups), a substituted orunsubstituted cycloalkyl having 5 to 10 carbon atoms in the carbocyclicring (such as cyclopentyl, cyclohexyl, 4-methylcyclohexyl, and4-chlorocyclohexyl), or a substituted or unsubstituted aryl group having6 or 10 carbon atoms in the aromatic ring (such as phenyl, naphthyl,p-methylphenyl, and p-chlorophenyl). Such groups can be substituted withone or more substituents such as alkyl, alkoxy, and halogen, or anyother substituent that a skilled worker would readily contemplate thatwould not adversely affect the performance of the polymeric binder inthe imageable element.

In Structure (Ie), R₃ is a substituted or unsubstituted linear orbranched alkyl group having 1 to 12 carbon atoms, or an aryl group (suchas phenyl or naphthyl group) that is substituted with an—O_(x)—(CH₂)_(y)—COOH group wherein x is 0 or 1 and y is 0, 1, or 2.Typically, x is 1 and y is 1, and the aryl group is a phenyl group. Thisaryl group can have further substituents such as alkyl, alkoxy, orhalogen that do not adversely affect the performance of the polymericbinder in the imageable element.

In Structure (If), R₄ is a substituted or unsubstituted aryl grouphaving 6 or 10 carbon atoms in the aromatic ring (such as phenyl ornaphthyl) and that can have one or more substituents such as alkyl,alkoxy, and others that a skilled worker would readily contemplate asnot adversely affecting the properties of the polymeric binder in theimageable element.

In addition to the second resins described above, the second inkreceptive layer can comprise a third water-insoluble, alkali-soluble or-dispersible resin that comprises a polysiloxane unit segment in apolyurethane or polyurethane urea backbone or side chain. Thepolysiloxane unit segments can be introduced into the resins by reactingat least one polyisocyanate with a compound having mono- or difunctionalterminal hydroxy or amine groups. Thus, the polysiloxane can be reactedwith siloxane diols or diamines in a polyaddition reaction.Alternatively, they can be introduced by using siloxane functionalizedisocyanates, or anhydrides can be used to introduce the polysiloxaneunit segments into polyurethane chains. Introduction of the polysiloxaneunit segments thus can be accomplished by either copolymerization orgrafting procedures (grafting the polysiloxane unit segments to a mainpolymer chain using acetalization) that are known in the art and suchintroduction of the desired moieties would be readily apparent to askilled worker in view of the teaching in this disclosure.

The term “polyisocyanate” refers to a compound that comprises two ormore isocyanate groups. In most embodiments, the polyisocyanate is adiisocyanate comprising two isocyanate groups.

In many embodiments, the third alkali solution-soluble or -dispersibleresin is a polyurethane or polyurethane urea that is derived from:

(i) reacting at least one polyisocyanate with a compound comprisingdifunctional terminal hydroxyl or amine groups, wherein thepolyisocyanate is functionalized with a polysiloxane segment, either inits main chain or a side chain, or

(ii) reacting at least one polyisocyanate with a compound comprisingmono- or difunctional terminal hydroxyl or amine groups, wherein thecompound also comprises polysiloxane segments either in its main chainor a side chain.

The polyurethane urea can also comprise a substituent having an acidichydrogen atom, for example, in specific polymer units. For example, thesubstituent having an acidic hydrogen atom can be selected from thegroup consisting of a carboxy group, —SO₂NHCOO— group, —CONHSO₂— group,—CONHSO₂NH— group, and —NHCONHSO₂— group. A carboxy group isparticularly useful. Multiple different substituents can be present inthe same molecule.

The polysiloxane moiety can have a linear, a partially branched,branched, or cyclic structure, and a linear structure is particularlyuseful. The linear polysiloxane moiety can be R₃SiO—(R₂SiO)i-R₂Si—,R₃SiO—(R₂SiO)j-R₂SiO— and similar groups that would be readily apparentto a skilled worker, wherein the R groups independently represent analkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 20carbon atoms, or an aralkyl group (aryl-substituted alkyl groups) having7 to 20 carbon atoms; and i and j are independently integers of from 1to and including 10,000. The noted alkyl groups include but are notlimited to, substituted or unsubstituted linear or branched alkyl groupssuch as a methyl, ethyl, n-propyl, iso-butyl, pentyl, hexyl, heptyl, andoctyl groups, and cycloalkyl groups such as substituted or unsubstitutedcyclopentyl and cyclohexyl groups. Also included are alkyl groups inwhich one or more hydrogen atoms bonded to the carbon atom(s) are atleast partially replaced with halogen atom(s) such as fluorine atom(s)or organic group(s) such as hydroxy, epoxy, glycidyl, acyl, carboxyl,amino, methacryl, and mercapto groups.

Useful aryl groups having 6-20 carbon atoms include but are not limitedto, substituted or unsubstituted phenyl, tolyl, xylyl, and mesitylgroups and aryl groups in which one or more hydrogen atoms bonded to thecarbon atom(s) thereof are at least partially replaced with halogenatom(s) such as fluorine atom(s) or organic groups such as hydroxy,epoxy, glycidyl, acyl, carboxyl, amino, methacryl, and mercapto groups.Useful aralkyl groups having 7 to 20 carbon atoms include but are notlimited to, substituted or unsubstituted benzyl and phenethyl groups aswell as aralkyl groups having 7 to 20 carbon atoms in which one or morehydrogen atoms bonded to the carbon atom(s) thereof are at leastpartially replaced with halogen atom(s) such as fluorine atom(s) ororganic group(s) such as hydroxy, epoxy, glycidyl, acyl, carboxyl,amino, methacryl group, and mercapto groups.

For example, the polyurethane comprising a polysiloxane segment in thebackbone or a side chain can be obtained from the reaction of (a) atleast one diisocyanate component, (b) at least one diol component thatcomprises a polysiloxane moiety, (c) at least one diol comprising asubstituent having an acidic hydrogen atom, and (d) optionally one ormore diols other than (b) and (c).

The molar ratio of the diisocyanate components (a) to the diolcomponents (b), (c), and (d) is generally from at least 0.7:1 to andincluding 1.5:1. When an isocyanate group remains at the end of thepolymer, it is possible to synthesize the resin by treating withalcohols or amines so that an isocyanate group does not finally remain.

The diisocyanate component is not limited as long as it comprises twoisocyanate groups. Examples of the diisocyanate component include butare not limited to, 4,4′-diphenylmethane diisocyanate, xylylenediisocyanate, naphthylene-1,5-diisocyanate, tetramethylxylenediisocyanate, hexamethylene diisocyanate, toluene-2,4-diisocyanate,toluene-2,6-diisocyanate, isophorone diisocyanate, hydrogenated xylylenediisocyanate, dicyclohexylmethane diisocyanate, norbomene diisocyanateand trimethylhexamethylene diisocyanate, and dimer acid diisocyanate.Mixtures of these compounds can also be used.

The diol comprising a substituent having an acidic hydrogen atom is notlimited but can have a group selected from the group consisting of acarboxy group, —SO₂NHCOO— group, —CONHSO₂— group, —CONHSO₂NH— group, and—NHCONHSO₂— group, with the carboxy group being particularly useful.

Diols having a carboxy group include but are not limited to,3,5-dihydroxybenzoic acid, 2,2-bis(hydroxymethyl)propionic acid,2,2-bis(hydroxyethyl)propionic acid, 2,2-bis(3-hydroxypropylpropionicacid, 2,2-bis(hydroxymethyl)acetic acid, bis-(4-hydroxyphenyl)aceticacid, 4,4-bis-(4-hydroxyphenyl)pentanoic acid and tartaric acid.2,2-Bis(hydroxymethyl)-propionic acid is particularly useful for itsreactivity with an isocyanate.

The amount of the diol comprising a substituent having an acidichydrogen atom is generally at least 10 weight % and up to and including95% weight %, or typically at least 20 weight % and up to and including90 weight %, relative to the total weight of the diol components.

The diol having a polysiloxane moiety in the backbone or a side chain isnot limited as long as it has the noted polysiloxane moiety. It isparticularly useful that it has no silicon atom-bonded hydroxy group.

In some embodiments, the compound in (ii) noted above is a diol that isused to prepare the third alkali solution-soluble or -dispersible resinthat has a polysiloxane segment in the backbone or a side chain, and isa hydroxy-modified di-oliganosiloxane having both terminal groupsrepresented by the following structure:—(C_(k)H_(2k))p-(OC_(m)H_(2m))q-(OC_(n)H_(2n))_(r)—(C₆H₄)_(s)—OH

wherein k, m, and n independently represent integers of from 1 to andincluding 3,

p represents an integer of 1 or more,

q represents 0 or an integer of from 1 to and including 100,

r represents 0 or an integer of from 1 to and including 100, and

s represents 0 or an integer of from 1 to and including 3.

In many embodiments, p represents an integer of from 1 to and including3 (or typically 1 or 2), q represents 0 or an integer of from 1 to andincluding 50 (or typically 0 or 1 to and including 30), r represents 0or an integer of from 1 to and including 50 (or typically 0 or 1 to andincluding 30), and s represents 0, 1, or 2 (or typically 0 or 1).

Useful terminal hydroxy-modified diorganopolysiloxanes can be obtainedfrom a number of commercial sources, including for example the productssold by Shin Etsu Chemical Co., Ltd. as X-22-160AS, KF-6001, KF-6002,KF-6003, X-22-4272, X-22-4952, X-22-6266, X-22-1821 and X-22-1824B.

In other embodiments, the compound in (ii) noted above is a diol that isused to prepare a second alkali solution-soluble or -dispersible resin,and has a polysiloxane segment in its backbone or a side chain, whichpolysiloxane segment is a diol-modified di-organopolysiloxane that isrepresented by the following structure:(R₁)₃SiO—[(R₁)₂SiO]_(t)—Si(R₁)₂R₂

wherein the multiple R₁ groups independently represent a substituted orunsubstituted alkyl group (having 1 to 20 carbon atoms includingsubstituted alkyl groups such as aralkyl groups) or a substituted orunsubstituted aryl group (having 6 to 20 total carbon atoms includingthe carbon atoms in the aromatic ring, such as substituted orunsubstituted phenyl or naphthyl groups including alkyl substitutedphenyl or naphthyl groups).

R₂ represents the following structure:—(C_(k)H_(2k))_(u)—(OC_(m)H_(2m))_(v)—(OC_(n)H_(2n))_(w)—(C₆H₄)_(x)—CR_(t)(R₃)₂

wherein k, m, and n independently represent integers of from 1 to andincluding 3,

u represents an integer or 1 or more,

v represents 0 or an integer of from 1 to and including 100,

w represents 0 or an integer of from 1 to and including 100, and

x represents 0 or an integer of from 1 to and including 3,

R₃ represents —(C_(y)H_(2y))_(z)OH wherein y represents an integer offrom 1 to and including 3 and z represents an integer of from 1 to andincluding 100, and

t represents an integer of from 1 to and including 10,000.

In some embodiments of R₂, u represent an integer of from 1 to andincluding 3 (typically 1 or 2), v represents 0 or an integer of from 1to 50 (typically 0 or an integer of from 1 to and including 30), wrepresents 0 or an integer of from 1 to 50 (typically 0 or an integer offrom 1 to and including 30), x represents 0 or 2 (typically 0), yrepresents 1 or 2, z represents an integer of from 1 to and including 30(typically 1 or 2), and t represents at least 100 and up to andincluding 10,000. The sum of v and w can be 1 in some embodiments.

Useful terminal hydroxy-modified diorganopolysiloxanes can be obtainedfrom various commercial sources including Shin Etsu Chemical Co., Ltd.such as products X-22-176DX and X-22-176F.

The third alkali solution-soluble or -dispersible resin is generallypresent in the second ink receptive layer in an amount of at least 1weight % and up to and including 40 weight %, and typically of at least3 weight % and up to and including 30 weight %, all based on the secondink receptive layer total dry weight.

The second ink receptive layer can also include one or more colorants asdescribed for example in U.S. Pat. No. 6,294,311 (Shimazu et al.)including triarylmethane dyes such as ethyl violet, crystal violet,malachite green, brilliant green, Victoria blue B, Victoria blue R, andVictoria pure blue BO. These compounds can act as contrast dyes thatdistinguish the non-exposed regions from the exposed regions in theimaged and developed precursor. The second ink receptive layer can alsooptionally include other contrast dyes, printout dyes, coatingsurfactants, dispersing aids, humectants, biocides, viscosity builders,drying agents, defoamers, preservatives, and antioxidants, all inamounts that are known in the art.

Other materials can be present in the outermost imageable layerincluding but not limited to, contrast dyes, coating surfactants,dispersing aids, humectants, biocides, viscosity builders, dryingagents, defoamers, preservatives, and antioxidants. Such materials canbe incorporated in amounts that would be readily apparent to a skilledworker in the art. For example, the following publications describeoptional components for the outermost imageable layer useful inpositive-working lithographic printing plate precursors: EP 1,543,046(Timpe et al.), WO 2004/081662 (Memetea et al.), U.S. Pat. No. 6,255,033(Levanon et al.), U.S. Pat. No. 6,280,899 (Hoare et al.), U.S. Pat. No.6,391,524 (Yates et al.), U.S. Pat. No. 6,485,890 (Hoare et al.), U.S.Pat. No. 6,558,869 (Hearson et al.), U.S. Pat. No. 6,706,466 (Parsons etal.), U.S. Pat. No. 6,541,181 (Levanon et al.), U.S. Pat. No. 7,223,506(Kitson et al.), U.S. Pat. No. 7,247,418 (Saraiya et al.), U.S. Pat. No.7,270,930 (Hauck et al.), U.S. Pat. No. 7,279,263 (Goodin), and U.S.Pat. No. 7,399,576 (Levanon), EP 1,627,732 (Hatanaka et al.), and U.S.Published Patent Applications 2005/0214677 (Nagashima), 2004/0013965(Memetea et al.), 2005/0003296 (Memetea et al.), and 2005/0214678(Nagashima) the disclosures of all of which are incorporated herein byreference.

The second ink receptive layer can further comprise one or moredevelopability enhancing compounds. A “developability-enhancingcompound” is an organic compound that, when added reduces the minimumexposure energy required to completely remove the ink receptive layer inthe exposed regions, in a suitable developer selected for that imageablelayer, relative to the minimum exposure energy required to completelyremove the same ink receptive layer in the exposed regions except forthe exclusion of the organic compound. This difference will depend up onthe particular organic compound and ink receptive layer compositionused. In addition, such organic compounds can also be characterized asnot substantially absorbing exposing radiation selected for theparticular ink receptive layer, and generally have a molecular weight ofless than 1000 g/mol.

Acidic Developability-Enhancing Compounds (ADEC), such as carboxylicacids or cyclic acid anhydrides, sulfonic acids, sulfinic acids,alkylsulfuric acids, phosphonic acids, phosphinic acids, phosphonic acidesters, phenols, sulfonamides, or sulfonimides can permit furtherimproved developing latitude and printing durability. Representativeexamples of such compounds are provided in [0030] to [0036] of U.S.Patent Application Publication 2005/0214677 (Levanon et al.).

The second ink receptive layer can also include adevelopability-enhancing composition containing one or moredevelopability-enhancing compounds (DEC) as described in U.S. PatentPublication No. 2009/0162783 (noted above). Still other usefuldevelopability-enhancing compounds are also described in thispublication using the following Structure (DEC₁):[HO—C(═O)]_(m)—B-A-[N(R₄)(R₅)]_(n)  (DEC₁)wherein R₄ and R₅ in Structure DEC₁ are independently hydrogen orsubstituted or unsubstituted alkyl groups, substituted or unsubstitutedcycloalkyl groups, or substituted or unsubstituted aryl groups, A is anorganic linking group that comprises a substituted or unsubstitutedphenylene directly attached to —[N(R₄)(R₅)]_(n), B is a single bond oran organic linking group having at least one carbon, oxygen, sulfur, ornitrogen atom in the chain, m is an integer of 1 or 2, n is an integerof 1 or 2. The “B” organic linking group can be defined the same as A isdefined above except that it is not required that B contain an arylenegroup, and usually B, if present, is different than A.

The one or more developability enhancing compounds described above canbe generally present in the second ink receptive layer in an amount ofat least 1 weight % and up to and including 30 weight %, or typically atleast 2 weight % and up to and including 20 weight %.

The second ink receptive layer generally also comprises thermally inertinorganic particles in an amount of at least 2 weight % and up to andincluding 20 weight %, or typically of at least 5 weight % and up to andincluding 15 weight %, based on the total dry weight of the second inkreceptive layer. These thermally inert inorganic particles generallyhave an average particle size of at least 0.5 nm and up to and including1000 nm, or typically of at least 50 nm and up to and including 500 nm.This average size can be determined using known particle evaluationequipment and procedures. The thermally inert inorganic particles aregenerally discrete, meaning that they are generally uniformly dispersedwithin the second resin(s). There can be minor amounts of clumping oragglomeration but such forms are not predominant. To achieve uniformdispersion of the inorganic particles, they are usually mixed wellwithin the second resin(s) using suitable mixing methods and equipmentincluding high shear mills and preparing a pre-dispersion that is thenintroduced into the second ink receptive layer formulation forapplication to the layer(s) below.

The term “thermally inert” means that the inorganic particles do notmeasurably add or detract from the infrared radiation imageability ofthe second ink receptive layer. Thus, these inorganic particles do notreact with the surrounding second resin(s) or other components in thesecond ink receptive layer to any appreciable extent.

Useful thermally inert inorganic particles include various particulatematerials that can be readily purchased from various commercial sources,or modified using known procedures. For example, useful materials ofthis type include but are not limited to, surface-modified silicaparticles such as fumed silica particles and sol-gel silica particles asdescribed for example in U.S. Pat. No. 8,043,787 (Hauck et al.). Otheruseful thermally inert inorganic particles include but are not limitedto, particles of calcium carbonate, zinc oxide, aluminum oxide, titaniumoxide, and zirconium oxide.

The second ink receptive layer can comprise thermally inert organicpolymer particles that are present in an amount of at least 0.1 weight %and up to and including 5 weight %, or typically of at least 0.2 weight% and up to and including 3 weight %, based on the total dry weight ofthe second ink receptive layer. Such thermally inert organic polymerparticles have an average particle size in μm that is at least 1.5times, or typically from 3 times and up to and including 10 times, theaverage dry coating weight of the second ink receptive layer in g/m².

Useful thermally inert organic polymer particles generally includeminimal inorganic components although the outer surface of the polymerparticles can be partially or wholly covered by inorganic materials suchas silica particles. Useful organic polymer particles of this type aredescribed for example in U.S. Pat. No. 8,383,319 (Huang et al.) whichorganic polymer particles comprise a core of crosslinked polymer(s) thatgenerally comprise at least 95% by volume of the organic particles. Theremaining amount of the organic polymer particles can comprise graftedhydrophilic polymeric surface groups that are formed on the crosslinked“core” by polymerizing hydrophilic monomers in the presence of thecrosslinked polymeric particles. Further details of such thermally inertorganic polymer particles are described in the noted patent that isincorporated herein by reference for such teaching.

Other useful thermally inert organic polymer particles aresilicate-coated particles having a crosslinked polystyrene core asdescribed in U.S. Pat. No. 7,097,956 (Miyamoto et al.) that isincorporated herein by reference.

The second ink receptive layer generally has a dry coating coverage (drycoating weight) of at least 0.2 g/m² and up to and including 2 g/m² ortypically of at least 0.4 g/m² and up to and including 1.5 g/m².

Infrared Radiation Absorbers:

One or more infrared radiation absorber (described above) can also bepresent in the precursors used in the present invention. Such infraredradiation absorbers can be in the first ink receptive layer, the secondink receptive layer, or both of the first and second ink receptivelayers. In still other embodiments, there can be an intermediate layerbetween the first and second ink receptive layers, and this intermediatelayer can also include one or more infrared radiation absorbers. In mostembodiments, the one or more infrared radiation absorbers are presentonly in the second ink receptive layer.

The infrared radiation absorber can be present in the precursor in anamount of at least 0.5 weight % and up to and including 20 weight % andtypically in an amount of at least 1 weight % and up to and including 5weight %, based on the total dry weight of the precursor (minus theweight of the substrate). As noted above, the infrared radiationabsorber can be located in one or more layers and the amount of theinfrared radiation absorber can be apportioned to the respective layersin a desired manner. The particular amount of a given compound to beused could be readily determined by one skilled in the art.

The one or more infrared radiation absorbers are sensitive tonear-infrared or infrared radiation, for example of at least 700 nm andup to and including 1400 nm and typically at least 750 nm and up to andincluding 1250 nm.

For example, useful infrared radiation absorbers include but are notlimited to, azo dyes, squarilium dyes, croconate dyes, triarylaminedyes, thioazolium dyes, indolium dyes, oxonol dyes, oxaxolium dyes,cyanine dyes, merocyanine dyes, phthalocyanine dyes, indocyanine dyes,indotricarbocyanine dyes, oxatricarbocyanine dyes, thiocyanine dyes,thiatricarbocyanine dyes, cryptocyanine dyes, naphthalocyanine dyes,polyaniline dyes, polypyrrole dyes, polythiophene dyes,chalcogenopyryloarylidene and bi(chalcogenopyrylo) polymethine dyes,oxyindolizine dyes, pyrylium dyes, pyrazoline azo dyes, oxazine dyes,naphthoquinone dyes, anthraquinone dyes, quinoneimine dyes, methinedyes, arylmethine dyes, squarine dyes, oxazole dyes, croconine dyes,porphyrin dyes, and any substituted or ionic form of the preceding dyeclasses. Suitable dyes are also described in U.S. Pat. No. 5,208,135(Patel et al.), U.S. Pat. No. 6,153,356 (Urano et al.), U.S. Pat. No.6,264,920 (Achilefu et al.), U.S. Pat. No. 6,309,792 (Hauck et al.),U.S. Pat. No. 6,569,603 (noted above), U.S. Pat. No. 6,787,281 (Tao etal.), U.S. Pat. No. 7,135,271 (Kawaushi et al.), and EP 1,182,033A2(noted above). Infrared radiation absorbing N-alkylsulfate cyanine dyesare described for example in U.S. Pat. No. 7,018,775 (Tao).

In addition to low molecular weight IR-absorbers, dyes having IR dyechromophores bonded to polymers can be used as well. Moreover, IR dyecations can be used as well, that is, the cation is the IR absorbingportion of the dye salt that ionically interacts with a polymercomprising carboxy, sulfo, phospho, or phosphono groups in the sidechains.

Near infrared absorbing cyanine dyes are also useful and are describedfor example in U.S. Pat. No. 6,309,792 (noted above), U.S. Pat. No.6,264,920 (Achilefu et al.), U.S. Pat. No. 6,153,356 (noted above), andU.S. Pat. No. 5,496,903 (Watanabe et al.). Suitable dyes can be formedusing conventional methods and starting materials or obtained fromvarious commercial sources including American Dye Source (Baie D'Urfe,Quebec, Canada) and FEW Chemicals (Germany).

Cyanine dyes having an anionic chromophore are also useful. For example,the cyanine dye can have a chromophore having two heterocyclic groups.In another embodiment, the cyanine dye can have from about two sulfonicacid groups, such as two sulfonic acid groups and two indolenine groupsas described for example in U.S Patent Application Publication2005-0130059 (Tao). Another general description of a useful class ofsuitable cyanine dyes is shown by the formula in [0026] of WO2004/101280 (Munnelly et al.).

Useful infrared radiation absorbers can also be pigments includingcarbon blacks such as carbon blacks that are surface-functionalized withsolubilizing groups. Carbon blacks that are grafted to hydrophilic,nonionic polymers, such as FX-GE-003 (manufactured by Nippon Shokubai),or which are surface-functionalized with anionic groups, such asCAB-O-JET® 200 or CAB-O-JET® 300 (manufactured by the Cabot Corporation)are also useful. Other useful pigments include, but are not limited to,Heliogen Green, Nigrosine Base, iron (III) oxides, manganese oxide,Prussian Blue, and Paris Blue. The size of the pigment particles shouldnot be more than the thickness of the imageable layer and desirably thepigment particle size will be less than half the thickness of theimageable layer.

Preparation of Positive-working Lithographic Printing Plate Precursors

The precursors used in the present invention can be prepared bysequentially applying a first ink receptive layer formulation onto theinterlayer (described above), and then applying a second ink receptivelayer formulation over the first ink receptive layer (usually whendried) using conventional coating or lamination methods. It is desiredto avoid intermixing of the first and second ink receptive layerformulations.

Thus the first and second ink receptive layers can be applied bydispersing or dissolving the desired components for each layer in asuitable coating solvent, and the resulting formulations aresequentially or simultaneously applied to the substrate (with theinterlayer) using suitable equipment and procedures, such as spincoating, knife coating, gravure coating, die coating, slot coating, barcoating, wire rod coating, roller coating, or extrusion hopper coating.The ink receptive layer formulations can also be applied by sprayingonto the substrate (with the interlayer).

The selection of solvents used to coat both the first and second inkreceptive layers depends upon the nature of the polymeric binders andother components in the layer formulations. To prevent the first andsecond ink receptive layer formulations from mixing or the first inkreceptive layer from dissolving when the second ink receptive layerformulation is applied, the second ink receptive layer formulationshould be coated from a solvent in which the polymeric binder(s) in thefirst ink receptive layer are insoluble.

Generally, the first ink receptive layer formulation is coated out of asolvent mixture of methyl ethyl ketone (MEK), 1-methoxy-2-propyl acetate(PMA), γ-butyrolactone (BLO), and water, a mixture of MEK, BLO, water,and 1-methoxypropan-2-ol (also known as Dowanol® PM or PGME), a mixtureof diethyl ketone (DEK), water, methyl lactate, and BLO, a mixture ofDEK, water, and methyl lactate, or a mixture of methyl lactate,methanol, and dioxolane.

The second ink receptive layer formulation can be coated out of solventsor solvent mixtures that do not dissolve the first ink receptive layer.Typical solvents for this purpose include but are not limited to, butylacetate, iso-butyl acetate, methyl iso-butyl ketone, DEK,1-methoxy-2-propyl acetate (PMA), iso-propyl alcohol, PGME, MEK andmixtures thereof.

After drying the layers, the lithographic printing plate precursors canbe further “conditioned” with a heat treatment for at least 40° C. andup to and including 90° C. for at least 4 hours usually in a stack ofmultiple precursors under conditions that inhibit the removal ofmoisture from the dried layers. During the heat treatment, thelithographic printing plate precursors are wrapped or encased in awater-impermeable sheet material to represent an effective barrier tomoisture removal from the precursors, or the heat treatment of theprecursors is carried out in an environment in which relative humidityis controlled to at least 25%. In addition, the water-impermeable sheetmaterial can be sealed around the edges of the precursors, with thewater-impermeable sheet material being a polymeric film or metal foilthat is sealed around the edges of the precursors.

In some embodiments, this heat treatment can be carried out with a stackcomprising at least 100 of the same lithographic printing plateprecursors, or when the precursor is in the form of a coil or web. Whenconditioned in a stack, the individual precursors can be separated bysuitable interleaving papers. The interleaving papers can be keptbetween the imageable elements after conditioning during packing,shipping, and use by the customer.

Imaging Conditions

During the method of this invention, the positive-working lithographicprinting plate precursor is exposed to a suitable source of exposinginfrared radiation depending upon the infrared radiation absorberpresent in the precursor to provide specific sensitivity that is at awavelength of at least 700 nm and up to and including 1400 nm, or morelikely of at least 750 nm and up to and including 1400 nm. Imagewiseexposing provides exposed regions and non-exposed regions in the firstink receptive layer and the second ink receptive layer.

For example, imaging can be carried out using imaging or exposingradiation from an infrared radiation-generating laser (or array of suchlasers). Imaging also can be carried out using imaging infraredradiation at multiple infrared wavelengths at the same time if desired.The laser used to expose the lithographic printing plate precursor isusually a diode laser, because of the reliability and low maintenance ofdiode laser systems, but other lasers such as gas or solid-state laserscan also be used. The combination of power, intensity and exposure timefor laser imaging would be readily apparent to one skilled in the art.

The imaging apparatus can be configured as a flatbed recorder or as adrum recorder, with the lithographic printing plate precursor mounted tothe interior or exterior cylindrical surface of the drum. An example ofan useful imaging apparatus is available as models of Kodak® Trendsetterplatesetters available from Eastman Kodak Company that contain laserdiodes that emit near infrared radiation at a wavelength of about 830nm. Other suitable imaging sources include the Crescent 42T Platesetterthat operates at a wavelength of 1064 nm (available from GerberScientific, Chicago, Ill.) and the Screen PlateRite 4300 series or 8600series platesetter (available from Screen USA, Chicago, Ill.) thatoperates at a wavelength of 810 nm.

Imaging with infrared radiation can be carried out generally at imagingenergies of at least 30 mJ/cm² and up to and including 500 mJ/cm² andtypically at least 50 mJ/cm² and up to and including 300 mJ/cm²depending upon the sensitivity of the imageable layer. With theseplatesetters, any imaging parameters such as the “surface depth”parameter of a Magnus 800 platesetter (Eastman Kodak Company) or the“focus” parameter of a PlateRite 4300 platesetter (Dainippon ScreenCompany), are decided by observing the difference in contrast betweenexposed regions and non-exposed regions in a stepwise imaging process.By using such as stepwise imaged lithographic printing plate precursor,a shortened printing run is possible and the obtained prints are alsouseful for determining such imaging parameters.

Development and Printing

After imaging, the imaged lithographic printing plate precursors can beprocessed “off-press” using a suitable processing solution describedbelow. When the positive-working lithographic printing plate precursorsare imaged and processed, the imaged (exposed) regions in the first inkreceptive layer and second ink receptive layer are removed duringprocessing while the non-exposed regions remain, revealing the grainedand anodized aluminum-containing substrate (as well as interlayer on thesubstrate).

In most embodiments, processing is carried out immediately after theimagewise exposing, thereby avoiding any post-exposure preheating step.

Development off-press can be accomplished using what is known as“manual” development, “dip” development, or processing with an automaticdevelopment apparatus (processor). In the case of “manual” development,development is conducted by rubbing the entire imaged precursor with asponge or cotton pad sufficiently impregnated with a suitable processingsolution (described below), and followed by rinsing with water. “Dip”development involves dipping the imaged precursor in a tank or traycontaining the appropriate processing solution for at least 10 secondsand up to and including 60 seconds (especially at least 20 seconds andup to and including 40 seconds) under agitation, followed by rinsingwith water with or without rubbing with a sponge or cotton pad. The useof automatic development apparatus is well known and generally includespumping a developer or processing solution into a developing tank orejecting it from spray nozzles. The imaged precursor is contacted withthe processing solution in an appropriate manner. The apparatus can alsoinclude a suitable rubbing mechanism (for example a brush or roller) anda suitable number of conveyance rollers. Some developing apparatusinclude laser exposure means and the apparatus is divided into animaging section and a developing section.

Thus, the processing solution (or developer) can be applied to theimaged precursor by rubbing, spraying, jetting, dipping, immersing, slotdie coating (for example see FIGS. 1 and 2 of U.S. Pat. No. 6,478,483 ofMaruyama et al.) or reverse roll coating (as described in FIG. 4 of U.S.Pat. No. 5,887,214 of Kurui et al.), or by wiping the outermost layerwith the processing solution or contacting it with a roller, impregnatedpad, or applicator. For example, the imaged precursor can be brushedwith the processing solution, or it can be poured onto or applied byspraying the imaged surface with sufficient force to remove thenon-exposed regions using a spray nozzle system (spray bar) as describedfor example in [0124] of EP 1,788,431A2 (noted above) and U.S. Pat. No.6,992,688 (Shimazu et al.). As noted above, the imaged precursor can beimmersed in the processing solution and rubbed by hand or with anapparatus. To assist in the removal of the back side coating, a brushroller or other mechanical component can be placed in contact with theback side coating during processing.

The processing solution can also be applied in a processing unit (orstation) in a suitable apparatus that has at least one roller forrubbing or brushing the imaged precursor while the processing solutionis applied. Residual processing solution can be removed (for example,using a squeegee or nip rollers) or left on the resulting lithographicprinting plate without any rinsing step. Excess processing solution canbe collected in a tank and used several times, and replenished ifnecessary from a reservoir. The processing solution replenisher can beof the same concentration as that used in processing, or be provided inconcentrated form and diluted with water at an appropriate time.

Useful processing solutions have a pH of at least 12 and up to andincluding 14, or more likely at least 12 and up to and including 13.7,or at least 12.5 and up to and including 14, and particularly when suchprocessing solutions are substantially free of silicate, meaning thatthey contain less than 0.5 weight % of silicates and metasilicates,based on total processing solution weight.

Particularly useful processing solutions are described in U.S. PatentApplication Publication 2012/0125216 (Levanon et al.) that isincorporated herein by reference. Such processing solutions generallyhave a pH of at least 12 and typically at least 12 and up to andincluding 14, or more likely at least 12.5 and up to and including 14.This highly alkaline pH is generally provided using one or more alkaliagents other than silicates and metasilicates. Useful alkali agentsinclude alkali metal hydroxides such as sodium hydroxide and potassiumhydroxide. Potassium ions can be more prevalent than the sodium ions andthe total amount of the alkali metal ions is generally at least 0.3gram-atom/kg and up to and including 1 gram-atom/kg.

It is also desirable for the processing solutions used in the practiceof the present invention are substantially free of non-reducing sugarsmeaning that the processing solution contains less than 1 weight % ofsuch compounds. Non-reducing sugars refers to compounds having noreducing properties due to the absence of free aldehyde group and ketonegroup. Non-reducing sugars can be classified into trehalose typeoligosaccharides prepared by linking reducing groups together,glycosides prepared by joining a reducing group of sugars withnon-sugars, and sugar alcohol prepared by reducing sugars withhydrogenation. Examples of such non-reducing sugars are provided in[0024]-[0026] of U.S. Patent Application Publication 2004/0063036 (notedabove).

These processing solutions can also include one or more metal cations(M²⁺) that are generally selected from the group consisting of barium,calcium, strontium, magnesium, nickel and zinc cation. Calcium,strontium, and zinc cations are particularly useful. The metal cationsM²⁺ are generally present in the processing solutions in an amount of atleast 0.0001 gram-atom/kg, and typically at least 0.001 gram-atom/kg andup to and including 0.01 gram-atom/kg. The desired cations can beprovided in the forms of various water-soluble salts that would bereadily apparent to one skilled in the art. Examples of such salts arecalcium chloride, barium chloride, strontium chloride, zinc acetate,calcium bromide, and calcium nitrate.

The processing solutions can also include one or more chelating agents,each of which has a complex formation constant (log K) for the M²⁺ metalcation of at least 3.5 and less than or equal to 4.5, and a log K foraluminum ion that is 7 or less. Useful chelating agents with theseproperties include but are not limited to, phosphono-polycarboxylicacids such as phosphonoalkyl polycarboxylic acids, such as2-phosphonobutane-1,2,4-tricarboxylic acid, which is particularly usefulwith calcium metal cations.

The described chelating agents can be present in an amount of at least0.01 mol/liter and up to and including 0.1 mol/liter, or typically atleast 0.03 mol/liter and up to and including 0.1 mol/liter.

A cationic surfactant or a betaine can also be present in the processingsolutions in an amount of at least 0.01 weight % and typically at least0.05 weight % and up to and including 3 weight %. Suitable cationicsurfactants for use in the present invention include, but are notlimited to, quaternary ammonium halides of fatty acids such as a fattyacid quaternary ammonium chloride. One example of such cationicsurfactants is provided in Hydromax 300 (Chemax Performance Products,Grenville, S.C.) that is described for example, in U.S. PatentApplication Publication 2006/0154187 (Wilson et al.) the disclosure ofwhich is incorporated herein by reference. Another useful cationicsurfactant is cetyl trimethyl ammonium chloride.

The processing solutions can also comprise one or more surfactants toachieve the best wetting, stabilizing, solubilizing, protecting,dispersing, and rinsing properties. Such surfactants are generallyanionic or nonionic in nature. Useful anionic surfactants are of thealkylaryl sulfonate class, such as an alkylaryl sulfonate, for example,alkyldiphenyloxide disulfonate that is available as Dowfax® 2 A1 fromDow Chemical Co. The anionic and nonionic surfactants can be present inan amount of at least 0.1 weight % and up to and including 2 weight %.

Other components of the processing solution include alkali metalhydroxides as alkali agent or one or more quaternary ammonium salts orone or more phosphonium salts, all in suitable amounts.

Particularly useful processing solutions have a pH of at least 12.5 andup to and including 14 and comprise calcium or strontium metal cations,a sodium or potassium hydroxide, 2-phosphonobutane-1,2,4-tricarboxylicacid, and a cationic surfactant.

Although each processing solution can also be used as its ownreplenisher, in addition, a specially formulated replenisher can beused. In the replenisher composition, the concentration of alkali agentis generally higher than the concentration of the alkali agent in theworking strength processing solution, to compensate for the consumptionof the alkali agent during the development process.

Following off-press development, the resulting lithographic printingplate can be baked with or without blanket or floodwise exposure to UVor visible radiation. Alternatively, a blanket UV or visible radiationexposure can be carried out, without a postbake operation.

Printing can be carried out by putting the imaged and developedlithographic printing plate on a suitable printing press. Thelithographic printing plate is generally secured in the printing plateusing suitable clamps or other holding devices. Once the lithographicprinting plate is secured in the printing press, printing is carried outby applying a lithographic printing ink and fountain solution to theprinting surface of the lithographic printing plate. The fountainsolution is taken up by the surface of the hydrophilic substraterevealed by the imaging and processing steps, and the ink is taken up bythe remaining regions of the outermost ink receptive layer. The ink isthen transferred to a suitable receiving material (such as cloth, paper,metal, glass, or plastic) to provide a desired impression of the imagethereon. If desired, an intermediate “blanket” roller can be used totransfer the ink from the lithographic printing plate to the receivingmaterial (for example, sheets of paper). The lithographic printingplates can be cleaned between impressions, if desired, usingconventional cleaning means.

The present invention provides at least the following embodiments andcombinations thereof, but other combinations of features are consideredto be within the present invention as a skilled artisan would appreciatefrom the teaching of this disclosure:

1. A method for forming a lithographic printing plate, the methodcomprising:

-   -   imagewise exposing a positive-working lithographic printing        plate precursor with infrared radiation to form an imaged        precursor comprising exposed regions and non-exposed regions,        and    -   processing the imaged precursor to remove the exposed regions        using a processing solution to provide a lithographic printing        plate,

wherein the positive-working lithographic printing plate precursorcomprises:

a grained and anodized aluminum-containing substrate,

a first ink receptive layer that is disposed over the grained andanodized aluminum-containing substrate, the first ink receptive layercomprising at least one water-insoluble, alkali solution-soluble or-dispersible first resin,

a second ink receptive layer disposed over the first receptive layer,the second ink receptive layer being the outermost layer in thepositive-working lithographic printing plate precursor, and comprising asecond resin that is a phenolic resin that is different from thewater-insoluble, alkali solution-soluble or -dispersible first resin,and

an infrared radiation absorber in an amount of at least 0.5 weight %, ineither or both of the first ink receptive layer and the second inkreceptive layer,

wherein the processing solution contains a metal cation M²⁺ selectedfrom barium, calcium, strontium, and zinc cations, has a pH of at least12, is substantially free of silicate, and is optionally substantiallyfree of reducing sugar.

2. The method of embodiment 1, wherein the second resin is a phenolicpolyvinyl acetal resin.

3. The method of embodiment 1 or 2, wherein the second ink receptivelayer further comprises thermally inert inorganic particles that arepresent in an amount of at least 2 weight % and up to and including 20weight %, based on the total dry weight of the second ink receptivelayer, which thermally inert inorganic particles have an averageparticle size of at least 0.5 nm and up to and including 500 nm.

4. The method of any of embodiments 1 to 3, wherein the second inkreceptive layer further comprises thermally inert organic polymerparticles that are present in an amount of at least 0.1 weight % and upto and including 5 weight %, based on the total dry weight of the secondink receptive layer, which thermally inert organic polymer particleshave an average particle size in μm that is at least 1.5 times averagedry coating weight of the second ink receptive layer in g/m².

5. The method of any of embodiments 1 to 4, wherein the positive-workinglithographic printing plate precursor further comprises:

a poly(vinyl phosphonic acid) interlayer, optionally comprisingphosphoric acid or a salt thereof comprising aluminum cation, disposeddirectly on the grained and anodized aluminum-containing substrate.

6. The method of embodiment 5, wherein the poly(vinyl phosphonic acid)interlayer has been derived by treating the grained and anodizedaluminum-containing substrate with a solution comprising poly(vinylphosphonic acid) and phosphoric acid.

7. The method of any of embodiments 1 to 6, wherein the infraredradiation absorber is present only in the second ink receptive layer.

8. The method of any of embodiments 1 to 7, wherein the second inkreceptive layer further comprises a third water-insoluble,alkali-soluble or -dispersible resin that comprises a polysiloxane unitsegment in a polyurethane or polyurethane urea backbone or side chain.

9. The method of any of embodiments 1 to 8, wherein the processingsolution comprises at least 0.0001 gram-atom/kg of a metal cation M²⁺selected from the group consisting of barium, calcium, strontium, andzinc cations.

10. The method of any of embodiments 1 to 9, wherein the metal cationM²⁺ is present in the processing solution in an amount of at least 0.001and up to and including 0.01 gram-atom/kg.

11. The method of any of embodiments 1 to 10, wherein the processingsolution further comprises a chelating agent that has a complexformation constant (log K) for the barium, calcium, strontium, or zincM²⁺ metal cation of at least 3.5 and less than or equal to 4.5, and acomplex formation constant (log K) for aluminum ion of 7 or less.

12. The method of any of embodiments 1 to 11, wherein the processingsolution further comprises a chelating agent that is aphosphono-polycarboxylic acid.

13. The method of embodiment 12, wherein the processing solutioncomprises 2-phosphonobutane-1,2,4-tricarboxylic acid.

14. The method of any of embodiments 1 to 13, wherein the processingsolution comprises an alkali metal hydroxide as an alkali agent.

15. The method of any of embodiments 1 to 14, wherein the processingsolution comprises a cationic surfactant.

16. The method of any of embodiments 1 to 15, wherein the processingsolution comprises one or more quaternary ammonium salts or one or morephosphonium salts.

17. The method of any of embodiments 1 to 16, wherein the processingsolution has a pH of at least 12.5 and up to and including 14, calciumor strontium metal cations, a sodium or potassium hydroxide,2-phosphonobutane-1,2,4-tricarboxylic acid, and a cationic surfactant.

18. The method of any of embodiments 1 to 17, further comprising bakingthe lithographic printing plate after the processing.

19. The method of embodiment 8, wherein the third water-insoluble,alkali-soluble or -dispersible resin further comprises a substituenthaving an acidic hydrogen atom.

20. The method of any of embodiments 1 to 19, wherein the first inkreceptive layer comprise water-insoluble, alkali solution-soluble or-dispersible first resin that comprises recurring units comprisingpendant tetrazole groups or recurring units derived from an alkoxymethyl(meth)acrylamide.

The following Examples are provided to illustrate the practice of thisinvention and are not meant to be limiting in any manner. The followingmaterials were used to prepare the lithographic printing plateprecursors used in the Examples:

-   BLO represents γ-butyrolactone.-   Byk® 307 is a polyethoxylated dimethylpolysiloxane copolymer that is    available from Byk Chemie (Wallingford, Conn.) or Altana, which is    used as a leveling agent.-   Polymer A is the same as Polymer A described in U.S. Pat. No.    8,088,549 (Levanon et al.) that is incorporated herein for this    material.-   Polymer B was a polymer derived from    methacylamide-N-tetrazole/methacrylic acid/N-methoxymethyl    methacrylamide/N-phenyl maleimide/acrylonitrile at a starting    monomer weight % of 15.0/4.2/12.6/23.5/44.7 and the polymer had an    acid number of 82 mg KOH/g polymer.-   Polymer C was a polyurethane resin made using dimethylolpropionic    acid/1,4 butanediol/KF-6001 silicon carbinole (from Shinetsu,    Japan)/4,4′-diphenylmethane diisocyanate in a weight ratio of    24/5.76/10.56/59.69.-   Polymer D was a polymer derived from methacrylamide, N-phenyl    maleimide, and methacrylic acid at a starting monomer weight % ratio    of 23.0/67.0/10.0 and Polymer D had an acid number of 65 mg KOH/g    polymer.-   Polymer E was a polymer derived from methacrylic acid,    N-(2-methacryloyloxyethyl)ethylene urea, methyl methacrylate, and    acrylonitrile at a starting monomer weight % ratio of    10.6/24.4/22.2/42.8 and Polymer E had an acid number of 69 mg KOH/g    polymer.-   Substrate A was a 0.3 mm gauge aluminum sheet that had been    electrochemically grained and anodized, having a Ra of 0.45 and that    had been treated with a solution containing 1.5 g/1 of poly(vinyl    phosphonic acid) using a spray bar process at 65° C. and 6 seconds    dwell time, followed by rinsing and drying, to provide a poly(vinyl    phosphoric acid) interlayer.-   Substrate B was a 0.3 mm gauge aluminum sheet that had been    electrochemically grained and anodized, having a Ra of 0.35 and that    had been with a solution containing 1.5 g/l of poly(vinyl phosphonic    acid) and 2 g/l of phosphoric acid using a spray bar process at    65° C. and 6 seconds dwell time, followed by rinsing and drying.-   Substrate C was a 0.3 mm gauge aluminum sheet that had been    electrochemically grained and anodized, having a Ra of 0.35 and that    had been treated with as solution to provide a phosphate/fluoride    interlayer (as described for example U.S. Patent Application    Publication 2012/0270152).-   Solvent Mixture L20 was a mixture of methyl ethyl ketone:Dowanol®    PM:BLO:H₂O:Dioxalane at a weight ratio of 45/20/10/10/15.-   Dowanol® PM is a glycol ether solvent available from Dow Chemical    Company.-   Resol LB9900 is copolymer of phenol and p-cresol from Momentive    (Germany).-   Particle A refers to silicate coated beads of a crosslinked    polystyrene derived from 70 weight % of styrene and 30 weight % of    divinyl benzene, particle size of ˜6 μm; See Columns 3-5 in U.S.    Pat. No. 7,097,956 (Miyamoto et al.) for further details.-   Particle B refers to a 10 w/w % dispersion of Aerosil® R9200    (Evonik) and Polymer A in a 9:1 weight ratio made by ball milling in    Dowanol® PM until 90% of the particles are smaller than 1.6 μm and    50% of the particles are smaller than 0.5 μm. The particle size    distribution curve has a maximum at around 0.42 μm when measured    with a Malvern Mastersizer X.-   IR Dye A is represented by the structure:

-   4-DMABA represents dimethyl aminobenzoic acid.-   Sudan Black is an azo dye having the structure:

-   Violet 612 is a visible dye having the structure:

-   Eosin has the structure:

The following materials were used in various developers (processingsolutions) used in the Examples:

-   Bayhibit® AM is 2-phosphonobutane-1,2,4-tricarboxylic acid (Lanxess)    used as a complexing agent for calcium cations.-   Hydromax™ 300 is an organic quaternary ammonium salt (PCC-Chemax).-   Dowfax® A1 is an alkyl diphenyl oxide anionic surfactant (Dow    Chemical Company).-   Sorbidex® 240 is a 70 wt. % aqueous solution of sorbitol    (non-reducing sugar).-   Synperonic® T304 is an ethylene/propylene oxide based on ethylene    diamine (Croda).

The following Developers (processing solutions) were prepared as shownbelow in TABLES I and II using the listed components (parts per 100):

Developers 1 and 8-10 are typical of the processing solutions useful inthe practice of the present invention.

Developer 2 and 3 were processing solutions like Developer 1 except thatcalcium ions were omitted.

Developer 4 was a processing solution like Developer 1 except thatHydromax® 300 was omitted.

Developers 5 and 6 were processing solutions containing a non-reducingsugar.

Developer 7 is a silicate-containing processing solution that iscommercially available as Kodak 300 Thermal Plate Developer (EastmanKodak Company) and is typically used to process imaged single-layerpositive-working lithographic printing plate precursors such as ElectraXD plates.

TABLE I Developer Developer 1 Developer 2 Developer 3 Developer 4Developer 5 Developer 6 Components Invention Comparative ComparativeComparative Comparative Comparative Deionized 91.39 91.80 91.51 91.4871.80 73.43 water Calcium 0.03 0 0 0.03 0 0 chloride 2x H₂O Bayhibit ®AM 0.38 0 0.38 0.38 0 0 Trisodium 1.50 1.50 1.50 1.50 1.50 0 citrate 2xH₂O Hydromax ™ 0.09 0.09 0 0 0.09 0 300 Dowfax ® 2A1 0.50 0.50 0.50 0.500.50 0 KOH 6.11 6.11 6.11 6.11 6.11 6.47 (45 wt. %) Sorbidex ® 240 0 0 00 20.00 19.90 Synperonic T- 0 0 0 0 0 0.20 304 EP1* 4.4 ml 4.7 ml 4.4 ml4.4 ml No data No data *Amount of 0.5 normal HCl used to titrate 5 ml ofdeveloper (processing solution).

TABLE II Developer 8 Developer 9 Developer 10 Developer ComponentsInvention Invention Invention Deionized water 91.75 91.31 91.01 Calciumchloride 2x H₂O 0.04 0.11 0.03 Bayhibit ® AM 0.50 0.38 0.76 Trisodiumcitrate 2x H₂O 0 1.50 1.50 Hydromax ™ 300 0.10 0.09 0.09 Dowfax ® 2A10.50 0.50 0.50 KOH (45 wt. %) 7.11 6.11 6.11 EP1* 4.1 ml 4.5 ml 4.4 ml*Amount of 0.5 normal HCl used to titrate 5 ml of developer (processingsolution).

Positive-working lithographic printing plate precursors were prepared asfollows with the noted layer structure and components:

A first ink receptive layer (Bottom Layer A) was prepared by coating aformulation prepared by dissolving 9.78 g of Polymer B and 0.2 g ofNaphthol Blue Black in 120 g of Solvent Mixture L20 onto Substrate A anddrying the coating at 80° C. for 2 minutes to provide a dry coatingweight of 0.8 g/m².

Another first ink receptive layer (Bottom Layer B) was prepared bycoating a formulation prepared by dissolving 9.6 g of Polymer D and 0.25g of Naphthol Blue Black in 120 g of Solvent Mixture L20 onto SubstrateA and drying the coating at 80° C. for 2 minutes to provide a drycoating weight of 0.8 g/m².

Still another first ink receptive layer (Bottom Layer C) was prepared bycoating a formulation prepared by dissolving 9.6 g of Polymer E and 0.25g of Eosin in 120 g of Solvent Mixture L20 onto Substrate A and dryingthe coating at 80° C. for 2 minutes to provide a dry coating weight of0.8 g/m².

A second ink receptive layer (Top Layer A) was prepared by applying aformulation prepared by dissolving 7.91 g of a 20 weight % solution ofPolymer A in Dowanol® PM, 1.35 g of Resol LB9900, 0.065 g of IR Dye A,0.026 g of Violet 612, 0.052 g of Sudan Black, 0.130 g of DMABA, 0.026 gof a 10% solution of Byk® 307 in Dowanol®, 0.130 g of Polymer C in 54.6g of a solvent mixture composed of methyl ethyl ketone (MEK), Dowanol®PM, and BLO at a 50:49:1 weight ratio and stirring in 0.967 g ofParticle B and 0.013 g of Particle A.

Another second ink receptive layer (Top Layer B) was prepared byapplying a formulation prepared by dissolving 8.04 g of a 20 weight %solution of Polymer A in Dowanol® PM, 1.35 g of Resol LB9900, 0.065 g ofIR Dye A, 0.026 g of Violet 612, 0.052 g of Sudan Black, 0.130 g ofDMABA, 0.026 g of a 10% solution of Byk® 307 in Dowanol® PM in 56 g of asolvent mixture composed of methyl ethyl ketone (MEK), Dowanol® PM, andBLO at a 50:49:1 weight ratio and stirring in 0.967 g of Particle B and0.013 g of Particle A.

Positive-working lithographic printing plate precursor (Element A) wasprepared by providing Top Layer A to provide a dry layer weight of 0.7g/m² on Bottom Layer A. The resulting precursors were then wrapped inaluminum laminated paper and conditioned for 2 days at 60° C. withinterleaf paper having a moisture content between 4.5% and 5.5% and 1day at room temperature.

Additional positive-working lithographic printing plate precursors(Elements B and C) were prepared in the same manner as Element A aboveexcept that the Substrates B and C, respectively, were used.

Positive-working lithographic plate precursor (Element D) was preparedin the same manner as Element A above except that the Top Layer A wascoated over the Bottom Layer B on Substrate B.

Positive-working lithographic plate precursor (Element E) was preparedin the same manner as Element A above except that the Top Layer B wascoated over the Bottom Layer B on Substrate B.

Positive-working lithographic plate precursor (Element F) was preparedin the same manner as Element A above except that the Top Layer B wascoated over the Bottom Layer C on Substrate B.

The following evaluations were made of Elements A-F:

Developer Resistance (Soak Test):

To assess the resistance of each precursor to specific developers(processing solutions), referred to as the Soak Test, drops of thedeveloper maintained as 25° C. were placed on the non-exposed precursorat 10 second time intervals and the developer was then rinsed off after90 seconds. The remaining % OD of the Top Layer coating was noted at 50seconds.

Developing Speed (Drop Test):

To assess the speed of development, each precursor was imaged at 15W/360 rpm (100 mJ/cm²). Drops of the developer maintained at 25° C. wereplaced on the outer surface of a strip of each exposed precursor at 2second intervals at various dwell times and rinsed off after 30 seconds.The tested regions were then partially inked. The minimum dwell timeshowing complete dissolution of the outer coating (non-inked Drop Test)and the inked region that was free of toning (inked Drop Test) werenoted.

Resistance of Substrate to Corrosion:

To assess corrosion resistance, a strip of each substrate, 2 cm×20 cmwas immersed in each developer at dwell times of 15 seconds up to 2minutes at 15 second increments. The change in the OD at 1 minute wasmeasured as a measure of corrosion, and the higher OD loss indicatedhigher corrosion.

Clear Point:

To assess the photospeed, each precursor was imaged with test patternscomprising solids and 8×8 checkerboard at 6 W to 18 W in steps of 1 Wusing a Creo Quantum 800 imagesetter (40 to 120 mJ/cm²). Each exposedprecursor was developed by placing it in a dish containing developer fora 10 seconds followed by rubbing the processed precursor with a softpaper tissue for 10 seconds and then rinsing the resulting lithographicprinting plate with water. The lithographic printing plates were driedand then evaluated for the clear point that is defined as the minimumenergy (mJ/cm²) to give a clear background.

Linearity:

Linearity was measured by imaging 50% Dots 8 pixel×8 pixel Checkerboard(each pixel represents a square in a 2400 dpi grid) on the precursorthat was imaged at 15 W 360 rpm. This was done by immersing the imagedprecursor in a bath of developer at 25° C. for 10 seconds and by rubbingit for 10 seconds with a soft tissue before rinsing off the precursorwith water. Each lithographic printing plate was dried and the 50% dotswere measured using a SpectoPlate Techkon densitometer. The lithographicprinting plate was considered linear when the 50% dot measured 50%±1%.

Results and Discussion:

The results of the performance evaluations of the Element A-F areprovided in the following TABLES III and IV.

TABLE III Drop Drop Substrate Test Test 50% Corrosion non- clean Rasterat Soak 1 minute inked inked Clear 100 mJ Developer Precursor Test ODloss (seconds) (seconds) Point [%] Invention 1 A 73% 0.001 8 10 53 49.1Example 1 Comparative 2 A  9% 0.192 6 >30 57 49.1 Example 1 Comparative3 A 55% 0.184 6 >30 57 49 Example 2 Comparative 4 A  2% 0.004 8 10 0 0Example 3 Comparative 5 A 98% 0.078 >30 not clean 140 99.8 Example 4Comparative 6 A 94% 0.077 16 >30 80 51.5 Example 5 Comparative 7 A 74%0.000 16 >30 50 48.5 Example 6 Invention 1 B 72% 0.001 8 10 53 49.5Example 2 Comparative 2 B 10% 0.190 6 >30 57 49.1 Example 7 Comparative3 B 52% 0.185 6 >30 57 49.6 Example 8 Invention 1 C 76% 0.002 8 10 5349.2 Example 3 Comparative. 2 C 11% 0.192 6 >30 57 49.4 Example 9Comparative 3 C 56% 0.190 6 >30 57 49.0 Example 10

TABLE IV Drop Drop Substrate Test Test 50% Corrosion non- clean Rasterat Soak 1 minute inked inked Clear 100 mJ Developer Precursor Test ODloss (seconds) (seconds) Point [%] Invention 1 D 63% 0.001 8 10 50 49Example 4 Comparative 2 D  7% 0.21 6 >30 55 48.9 Example 11 Comparative3 D 24% 0.181 6 >30 54 49 Example 12 Invention 1 E 43% 0.001 6-8 8 5048.5 Example 5 Comparative. 2 E  3% 0.212 6 >30 49 48.9 Example 13Comparative 3 E 19% 0.191 6 >30 51 48.1 Example 14 Invention 1 F 78%0.001 8 8-10 57 50.1 Example 6 Comparative. 2 F  9% 0.199 6-8 >30 5949.1 Example 15 Comparative. 3 F 53% 0.191 8 >30 55 45.0 Example 16Invention 8 A 70% 0.003 8 10 53 48.4 Example 7 Invention 9 A 79% 0.001 8-10 10-12 54 49.9 Example 8 Invention 10 A 71% 0.005 6-8 10 53 48.9Example 9

The results provided in TABLES III and IV show that Developers 1 and8-10 provided the optimum results for processing the imagedpositive-working lithographic printing plate precursors according to thepresent invention, thereby providing a good image and clean backgroundwithout any corrosion of the substrate (that can lead to toning).

The results also show that the absence of calcium cations and Bayhibit®AM in Developer 2 (see Comparative Examples 1, 7, and 9) made thedeveloper (processing solution) very aggressive towards the inkreceptive layer coatings and the precursor substrate. In addition, theinked Drop Test showed that without the calcium cations, the imaged anddeveloped regions on the lithographic printing plate exhibited toning.

Only calcium cations were omitted from Developer 3. As seen by the EP1values in TABLE I, the alkalinity was reduced relative to that ofDeveloper 2 as part of the potassium hydroxide was neutralized by the2-phosphonobutane-1,2,4-tricarboxylic acid (Bayhibit® AM). Therefore,Developer 3 provided good images after development even without thepresence of calcium cations. However, the substrate corrosion wassignificant, causing toning upon inking (for example, see ComparativeExamples 2, 8, and 10).

Omitting the quaternary ammonium salt as in Developer 4 (ComparativeExample 3) caused a strong attack on the image in the lithographicprinting plate and thus Developer 4 is not a useful processing solutionfor the positive-working lithographic printing plates designed for thepresent invention.

The use of Developers 5 and 6 represent typical use of a non-reducingsugar and the resulting Drop Tests were too slow. Developer 5 was tooweak to develop the imaged precursor and also showed significantsubstrate corrosion (Comparative Example 4).

Developer 6 provided development at much higher energy and againexhibited significant substrate corrosion (Comparative Example 5).

Developer 7 (Comparative Example 6) was a typical silicate-containingdeveloper and it caused no substrate corrosion but exhibited poorerdevelopment speed.

Although silicate-containing developers are frequently used in the art,the main disadvantage of their use is the dirtiness of the developmentprocessor that occurs due to silicate deposits. These problems becameworse when Elements A and B were processed in large volumes. Thepoly(vinyl phosphonic acid) interlayer had been applied onto theelectrochemically grained and anodized aluminum-containing substratesthrough a spray bar process for convenience only from the upper side ofthe substrate. The backside of the substrate was thus not protected bythe interlayer and therefore some substrate corrosion occurred,resulting in the formation of aluminum silicate sludge in the processor.Element C is, having the desired interlayer application, was lesssusceptible to substrate corrosion. However, for the ease ofmanufacturing Substrates A and B are desirable substrates.

Further, it can be seen that although the Substrates B and C were morecorrosion resistant compared to Substrate A, omitting calcium cationsfrom Developers 2 and led to significant substrate corrosion and thustoning was evident.

The invention has been described in detail with particular reference tocertain specific embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

The invention claimed is:
 1. A method for forming a lithographicprinting plate, the method comprising: imagewise exposing apositive-working lithographic printing plate precursor with infraredradiation to form an imaged precursor comprising exposed regions andnon-exposed regions, and processing the imaged precursor to remove theexposed regions using a processing solution to provide a lithographicprinting plate, wherein the positive-working lithographic printing plateprecursor comprises: a grained and anodized aluminum-containingsubstrate, a first ink receptive layer that is disposed over the grainedand anodized aluminum-containing substrate, the first ink receptivelayer comprising at least one water-insoluble, alkali solution-solubleor -dispersible first resin, a second ink receptive layer disposed overthe first receptive layer, the second ink receptive layer being anoutermost layer in the positive-working lithographic printing plateprecursor, and comprising a second resin that is a phenolic resin thatis different from the water-insoluble, alkali solution-soluble or-dispersible first resin, and thermally inert inorganic particles thatare present in an amount of at least 2 weight % and up to and including20 weight %, based on the total dry weight of the second ink receptivelayer, which thermally inert inorganic particles have an averageparticle size of at least 0.5 nm and up to and including 500 nm, and aninfrared radiation absorber in an amount of at least 0.5 weight %, ineither or both of the first ink receptive layer and the second inkreceptive layer, wherein the processing solution contains a metal cationM²⁺ selected from barium, calcium, strontium, and zinc cations, has a pHof at least 12, is substantially free of silicate, and is optionallysubstantially free of reducing sugar, and wherein the processingsolution further comprises one or more quaternary ammonium salts or oneor more phosphonium salts.
 2. The method of claim 1, wherein the secondresin is a phenolic polyvinyl acetal resin.
 3. The method of claim 1,wherein the second ink receptive layer further comprises thermally inertorganic polymer particles that are present in an amount of at least 0.1weight % and up to and including 5 weight %, based on the total dryweight of the second ink receptive layer, which thermally inert organicpolymer particles have an average particle size in μm that is at least1.5 times average dry coating weight of the second ink receptive layerin g/m².
 4. The method of claim 1, wherein the positive-workinglithographic printing plate precursor further comprises: a poly(vinylphosphonic acid) interlayer, optionally comprising phosphoric acid or asalt thereof comprising aluminum cation, disposed directly on thegrained and anodized aluminum-containing substrate.
 5. The method ofclaim 4, wherein the poly(vinyl phosphonic acid) interlayer has beenderived by treating the grained and anodized aluminum-containingsubstrate with a solution comprising poly(vinyl phosphonic acid) andphosphoric acid.
 6. The method of claim 1, wherein the infraredradiation absorber is present only in the second ink receptive layer. 7.The method of claim 1, wherein the second ink receptive layer furthercomprises a third water-insoluble, alkali-soluble or -dispersable resinthat comprises a polysiloxane unit segment in a polyurethane orpolyurethane urea backbone or side chain.
 8. The method of claim 1,wherein the processing solution comprises at least 0.0001 gram-atom/kgof a metal cation M²⁺ selected from the group consisting of barium,calcium, strontium, and zinc cations.
 9. The method of claim 8, whereinthe metal cation M²⁺ is present in the processing solution in an amountof at least 0.001 and up to and including 0.01 gram-atom/kg.
 10. Themethod of claim 8, wherein the processing solution further comprising achelating agent that has a complex formation constant (log K) for thebarium, calcium, strontium, or zinc M²⁺ metal cation of at least 3.5 andless than or equal to 4.5, and a complex formation constant (log K) foraluminum ion of 7 or less.
 11. The method of claim 8, wherein theprocessing solution further comprises a chelating agent that is aphosphono-polycarboxylic acid.
 12. The method of claim 1, wherein theprocessing solution comprises 2-phosphonobutane-1,2,4-tricarboxylicacid.
 13. The method of claim 1, wherein the processing solutioncomprises an alkali metal hydroxide as an alkali agent.
 14. The methodof claim 1, wherein the processing solution comprises a cationicsurfactant.
 15. The method of claim 1, wherein the processing solutionhas a pH of at least 12.5 and up to and including 14, calcium orstrontium metal cations, a sodium or potassium hydroxide,2-phosphonobutane-1,2,4-tricarboxylic acid, and a cationic surfactant.16. The method of claim 1, further comprising baking the lithographicprinting plate after the processing.
 17. The method of claim 7, whereinthe third water-insoluble, alkali-soluble or -dispersible resin furthercomprises a substituent having an acidic hydrogen atom.
 18. The methodof claim 1, wherein the first ink receptive layer comprisewater-insoluble, alkali solution-soluble or -dispersible first resinthat comprises recurring units comprising pendant tetrazole groups orrecurring units derived from an alkoxymethyl (meth)acrylamide.